The Influence And Mechanism Research On Thermal Fluctuation Of The Mixing Of Hot And Cold Fluids In T-Junction With Additional Structure

As the structure that fluids connected and mixed, T-junction has been widely used in the field of industrial production, energy, chemical, biological and other industrial process due to its advantages of simple processing, convenient arrangement and so on. In different operating conditions, T-junction suffered impacts produced by the temperature fluctuation of fluids mixing process with different temperature, resulting in alternating thermal stress eventually. With the long-term effects of that, thermal fatigue failure on the T-pipe will happened, which will cause a serious security threat of nuclear piping system and even the entire nuclear power plant. The number of fatigue crack in pipeline、valve leakage caused by thermal fatigue is more than one hundred around the world. With the rapid development of China’s nuclear power industry, the pipeline failure problem caused by thermal fatigue and thermal fluctuations has attracted wide attention. Therefore, it has important scientific and realistic sense for prolonging the service life of equipment and safety evaluation, optimization design of nuclear piping system to study the mechanism of thermal fatigue in T-junction and weakening method.This study constructed the flow and heat transfer experimental device of hot and cold water and carried out experiments with four different branch pipe structures in three jet conditions:wall jet, deflecting jet and impinging jet. We measured temperature in the the above conditions, and tracking the whole process with indicator. The experimental results show that the tapered tube structure have a significant effect on reducing thermal fluctuations of the wall in the mixing process.Based on the experimental conditions, large eddy simulation about the mixing of hot and cold fluids was carried out in the Fluent platform. The comparison of numerical results and experimental results shows that they are in good agreement with each other, which indicate that the mathematical model and numerical simulation has certain accuracy and reliability on pridicting the process of mixing in T-junction.Based on the verification of large eddy simulation, the numerical calculations of T-junction in different conditions were performed and the numerical outcomes were analyzed. The numerical outcomes show that: the tapered tube structure can effectively reduce the temperature fluctuation in the mixing process and can enhance the mixing efficiency in the tube at the same time.This study explored the effects of different branch pipe structures on the thermal fluctuations in mixing process of hot and cold fluids, and laid a theoretical foundation for revealing the mechanism of reducing thermal fluctuation in mixing process,which providing a scientific basis for the optimization design and avoiding thermal fatigue in T-junction.